The present invention pertains to a buckle used in a seat belt device provided for a seat of a vehicle, such as an automobile.
Currently, in various vehicles including automobiles, seat belt devices for protecting occupants in emergency, such as collision, are installed on seats thereof. In order to facilitate the occupant to wear on and off such a seat belt, a buckle is normally provided. In general, the buckle comprises a latch member provided with a joggle portion which engages a tongue, wherein the latch member is biased by a spring in such a direction as to engage the tongue.
In this case, when the spring force against the latch member is set to be weak in order to reduce the operating force for releasing the engagement between the tongue and the buckle, the force for keeping the engagement between the tongue and the latch member is weak. On the other hand, when the spring force against the latch member is set to be strong in order to increase the force for keeping the engagement between the tongue and the latch member, the operating force required for releasing the engagement is increased.
Therefore, the buckle is provided with a lock member which prevents the displacement of the latch member during the engagement with the tongue, thereby minimizing the spring force against the latch member and thus reducing the operating force for releasing the engagement. This technique has been used conventionally.
On the other hand, various seat belt devices having buckle pretensioners connected to the buckles have been proposed. The buckle pretensioner is actuated in case of emergency, such as a vehicle collision, to rapidly pull the buckle so that the seat belt device can quickly restrain a vehicle occupant.
Various seat belt devices having the buckles with the lock members and the buckle pretensioners also have been proposed.
By the way, in such a seat belt device including the buckle with the lock member and the buckle pretensioner, there is a possibility that an unexpected release due to inertia, so-called xe2x80x9cinertia releasexe2x80x9d arises because, when the buckle is suddenly stopped at the end of pretensioning by the buckle pretensioner, due to large inertia, an operational button and the lock member will continue to move toward their release positions where the engagement between the tongue and the buckle is released. Therefore, to prevent such inertia release, the seat belt device is provided with movement prevention means for preventing such movement of the operational button and the lock member toward their release positions.
However, such movement prevention means used in the buckle of the conventional seat belt device has problems that its structure is complex and that its operation is not reliable.
The present invention has been made for solving the above problems and an object of the present invention is to provide a buckle which can effectively prevent the inertia release with improved reliability of operation.
Another object of the invention is to provide a buckle as stated above, wherein the structure is simple.
To solve the aforementioned problems, the present invention provides a buckle comprising: a base having side walls; a latch member which is supported by the side walls such that the latch member can pivot between an unlatched position and a latched position, and when a tongue is inserted to a predetermined position, the latch member pivots to the latched position to engage the tongue; an operational member for releasing an engagement between the tongue and the latch member; a lock member which is movable between an unlocked position and a locked position, is set in the locked position to hold the latch member in the latched position when the tongue is engaged by the latch member, and is moved by the operational member into the unlocked position to allow the engagement between the tongue and the latch member to be released; and movement prevention means for preventing the operational member and the lock member from moving into such position as to allow the engagement between the tongue and the latch member to be released when the operational member and the lock member are subjected to large inertia force.
The movement prevention means is disposed between the side walls in such a manner that the movement prevention means is movable in the longitudinal direction of the buckle and pivotable, and comprises a mass body, in which the center of gravity is arranged eccentrically relative to the pivot shaft of the movement prevention means, and a lever for preventing the look member from moving into the unlocked position. The lever is out of the path of movement of the lock member when the lock member is set in the unlocked position, and is in the path of movement of the lock member when the lock member is set in the locked position. When inertia force is exerted in a direction opposite to a direction of releasing the engagement between the tongue and the latch member, the movement prevention means moves in the longitudinal direction so as to prevent the pivotal movement of the movement prevention means due to the inertia force acting on the center of gravity of the mass body. When inertia force is exerted in the direction of releasing the engagement between the tongue and the latch member, a moment acting on the movement prevention means in a direction of holding the lever in the path of movement of the lock member is produced by the inertia force acting on the center of gravity of the mass body and a moment acting on the movement prevention means in a direction moving the lever to come off the path of movement of the lock member is produced by the inertia force of the operational member. The mass body is designed in such a manner that the moment produced by the inertia force acting on the center of gravity of the mass body is larger than the moment produced by the inertia force of the operational member.
In the buckle according to the present invention structured as mentioned above, when the buckle is pulled by a buckle pretensioner, inertia force acts on the center of gravity of the mass body, whereby the movement prevention means is prevented from pivoting in a direction of moving the lever to come off the path of movement of the lock member. Since the mass body is designed in such a manner that the moment produced by the inertia force acting on the center of gravity of the mass body is larger than the moment produced by the inertia force of the operational member, these moments being produced at the end of pretensioning travel by the buckle pretensioner when the buckle is suddenly stopped, the movement prevention means is prevented from pivoting in a direction moving the lever to come off the path of movement of the lock member. In this manner, the inertia release can be securely prevented.
In this case, the movement prevention means is composed of only the mass body and the lever, thereby simplifying the structure thereof.